onboarding: auto-create default checks when entity is created

Three insertion points:
- CreateEntity (POST /api/v1/entities)
- EnrollClient (POST /api/v1/clients/enroll)
- seed.go (seed ingest at deploy time)

Shared logic in internal/checkdefaults — resolves host IP from
lan_ip > mesh.netbird.ip > mesh_ip, SSH user/port from attributes.

Default checks per entity type:
- proxmox-host/standalone-server: ping + cpu + memory + load + disk + updates
- workstation: ping + cpu + memory + load
- lxc: cpu + memory + load + disk
- vm: ping
- service: process_check.sh

All idempotent (ON CONFLICT DO NOTHING). New machines now get
monitoring automatically — no manual curl calls needed.

internal/db/seed.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 
+	"github.com/dtoro/oikos/internal/checkdefaults"
 	"github.com/google/uuid"
 	"github.com/jackc/pgx/v5"
 )
@@ -143,6 +144,8 @@ func IngestInventorySeed(ctx context.Context, tx pgx.Tx, data map[string]any) (*
 			return nil, fmt.Errorf("entity_status %s: %w", slug, err)
 		}
 
+		checkdefaults.Ensure(ctx, tx, entityID, slug, typeName, attrsBytes)
+
 		r.Entities++
 	}